The second of a thousand steps, and what I use to exclude (or include) options at the outset is a rough outline that I draft in Apple's Pages app. I worked in computers when PageMaker was introduced, and was subsequently rendered obsolete ~ as were WANG Word Processors ~ by the improved functionality of programs like Pages and Word.
I have been known to sketch these outlines on the workshop floor (as indeed they did in chalk at the time the Titanic was built) but this is quicker, less messy and equally enjoyable.
Here we can see straight away that the eight-ball layout is not as attractive as might first appear, bearing in mind that each pair of propellers rotates the same way. There is no problem with this if the cantilevers are extended to 18" around the 14" centre-section.
Left as close as they can be to the centre-section as in the lower half of the diagram, however, then diagonally adjacent propellers rotate efflux in the same direction; which is decidedly inefficient. Note incidentally that from the top each pair of propellers has to rotate clock-, anti- clock- and anti-clockwise in conventional quadcopter practise.
Benefits of the layout are a compact foot-print along with a concentrated entrainment of downdraught that adds to efficiency in the hover... whilst disadvantages include the fact the spars do not lie in the same plane unless separate cantilevers are attached to four-way connectors at each corner of the central square: which at any scale adds the the cost of specialised product that might otherwise not be necessary.
The choice as often as not in designing eVTOLs lies in that between 'geeks' and 'jocks'. One of these might not look the part but passes aerodynamics with distinction, whilst the other goofs the exams but eminently looks the part.
What we choose going forward is thus divided between two goals viz. do we want the most economical means possible to get airborne, albeit at an acceptable level of risk given a single component failure? Or do we want to design a commercial product a la Blackfly's Opener or Jetson's One from the get-go...
...that comes neither cheap nor quickly?
